Equipment for testing trolley wire insulators and rail bonds of electric railways



Patented Aug. 8, 1950 'VSEQUIPMENT FOR TESTING TROLLEY WIRE INSULATORS AND RAIL BONDS OF ELEC- 'r no RAILWAYS Andrew Sorenseh, Edgewood, Pa., assignor to The Union-Switch & Signal Company, Swiss-i vale, 2a., a corporation of Pennsylvania Application July 23, 1947, Serial No. 762,850

My invention relates t equipment for testing' trolley wire insulators and rail bonds of electric railways, and more particularly tosuch testing equipment for electric railways in mines.

:In mines an electric railway for hauling out the coal or ore generally-uses a trolley wire suspended from the roof of the mine by hangers which are spaced atfrequent intervals and each of which includes an insulator. The propulsion current circuit..comprises the trolley wire and the bonded railsand generally uses direct current of 20.0 to 600- VOltSL" The roof of the mine comprises earth, rock and-other material and a faultyinsulator of a hanger may result in the full voltage-of the'propulsion currentbeing impressed between the trolley wire and ground with the result a. relatively large current may flow from the trolleywire into the roof and from there through theground path to the return rail system. Thezheat developed at a faultyhanger due to this relatively large current-flowing to ground. can'be intense enough to start a fire because of the combustible'material that usually accumulates about-the roof of: a mine. Such fire tends to cause explosion and other danger to the miners. Furthermore, the leakage is a loss of powerand when a number of hangers become faulty, the leakage current may be large en ugh to impair the operation of the railway.

Again, a broken or defective rail bond tends to materially, increase the resistance of the propulsion currentcircuit and to unbalance the distribution of thepropulsion current in the rails. Av number'of broken and defective rail bonds may so increase the'resistance of the rail return as to reduce the voltageavailable for the locomotive motors to a point where the loss of:power materiallyaffects; the operation of the locomotive. The rail bonds of amine track aresubjected to a great deal-of strain due to the fact that the roadbed of any mine track is not as a-rule in very good-condition.

It is therefore in the interest of safety and economy that tests of the trolley wire insulators and the rail bonds be made frequently, and such testing of the trolley wire insulators and rail bondsin a minetrack is laborious and an expensiveitem in the maintenance.

- -Accordingly, a feature of my invention is the provision of novel-and useful test equipment for detecting faulty trolley wire insulators and rail bonds of electric railways 1 Another feature of my invention is the provision of improved test equipment capable of being mounted upon a mine locomotive or other vehicle 'I '2 Claims. (01. -183) for automatically detecting faulty trolley wire hangers'and rail bonds as the vehicle moves over the minetrackn I x .1 Other features, objects andadvantagesofrmy invention will appear I as the; specification .1 progreSSeS. .r

To attain the'foregoing'feature's, objects and advantages of my invention; I provide onalocomotive or other vehicle r of. an :electric irailway, a source of alternating current, one terminal; of which source preferably. connected to the trolley wire through-a trolley wheel andgthe other terminal of which. source islconected to the rails through the frame'and wheels of the locomotive or vehicle. in thisway the alternating current is applied to the:circuit network which includes the trolley wire andthe rails. The alternating current to be-used ispreferably of arelatively high frequency, such-as';.for example, 10,000 cycles persecondor higher, and current of an eiTective value flows in the trolley wire from the point at whichit is appliedthereto and returns through the tw rails in multiple due to the distributed capacitance of. the trolley wire and the rails. i 1.

Two receiving circuits are mountedon the vehicle for inductively receiving energy from the trolley wire. These two receiving-circuits are preferably alike and include pick-up coils which are symmetrically spaced in a common plane relatively close to the trolley wire to have substantially the same inductive relationship to the trolleywire. These two receiving circuits are balanced in such a way that the electromotive forces induced in the two pick-up coils are equal and balance out when the sameivalueof alternating current flows in the trolley wire past each pick-up coil. However, 'theielectromotive forces are unequal, and an electromotive :force equal to the difference of the two appears'when the receiving coils are spaced on opposite sides of a hanger having taultyihsulator. This'is so because a portion of the alternating current flows through the broken downinsul'atorinto the roof of the mine, and more current flows paston'e coil than the other. This unbalanced condition of the two receiving circuits causes the'operation of an indicator to indicate the presence of the broken down insu1ator.- Y

Two other receiving circuits are provided on the locomotive or vehicle for detecting faulty rail bonds. These two receiving circuits include two pick-up coils, one for each-circuit and which coils are'mounted one over each rail." These two receiving circuits are arranged' 'in such a way 3 that when approximately the same electromotlve forces are induced in the pick-up coils due to approximately equal values of the alternating testing current flowing in the two rails, the two electromotive forces cancel, but that when a rail joint having aabroken. bond passes under one .or the other of the: pick-up coils the testing currents are unequal the unequal electromotive forces induced in the pick-up coils no longer cancel, and the unbalancedportion of the electromotive forces is applied; to. an indicator to loss of power to become so great as to overload the generator to the extent that the operation of 'the'mine raflway'is seriously impaired.

indicate the presence of the faulty rail bond.

These two indicating devices may be independent, but I prefer to use an indicator in the .form of a twin electron ray tube so that. the operator needs but look at the one indicatingelementto" observe the two indications the locomotive moves through the mine, one shadow angle of the electron ray tube indicating faulty"insula-- tors and the other shadow angle of the tube indicating iaulty rail bond-s.

For: a. fuller: understanding of my invention, reference may be had to the accompanying; drawlugs. and theaccomparrying: description thereof, Fig- 1 of the drawings; being a diagrammatic view showing one form of the test equipment embodying my invention when mounted on a locomotive of an electric mine railway;..and Fig. 2. being a diagrammatic. view showing. another form of the apparatus. for detecting faulty .rail; bonds, and which apparatus can be. used for the corresponding portion of. the. equipment of Fig. 1.

In each. of the .two. views, like reference char: acters. are used to designatesimilarparts.

It. is to be. understood that. the: .invention is not limited to a mine; railway, and this one. anplination. of the equipment serves to illustrate the many places; the. equipment is: usefuL.

Referring to Fig.1, the reference character MT designates the. track .of an electric: railway of a the two rails. Id and lboi"v the track being shown in. section at. the. right-hand end of the drawing for reasons that: will become apparent hereinafter- The. reference: character TWdesignates a trolley wire of the electricrailway. This trolley wire TW is suspended by hangers. HA spaced at frequent intervals; there being .three such hangersil lustrated in the drawing. In the usual arrangement. each hanger HA is secured to the roof of the mine by suitable fasteners securedin the rocks and earth forming the roof. These hangers may beef any standard and suitable form, and each includes an insulator l0, so that. the trolley wire TW is normally insulated from the. mine root, that is, it is. normally insulatect from groundw A. propulsion power source, usually in the form or a direct current generator, not. shown, has one terminalconnected to. the trolley wire and its. other terminal: connected. to the two rails in and lb, the rails. being bonded in the. usuaLmannor to complete the return circuit pathfor the propulsion currents To. aid in the understanding of the. invention, Ishailassume. thatv the propulsion. current is. a direct current of 250 volts, but other currents and voltages can be used.v It. is clear that. as: long as. the insulator ID of each banger HA is. intact, little or no propulsion current leaks from the trolley. wire to ground through the mine: roof, but. that. if. one of the insulators .i It becomes short. circuited substantially; the full voltage of; the. propulsion current source impressed between the. trolley wire TW and ground and a. relatively large current leaks throughthe mine root; As stated hereinbefore,

Furthermore, it is clear that if the bonding of the rails la'and lb is in good condition, the propulsion current will divide approximately equally in the two rails, and a minimum resistance "in the'rail'return'path is present but that a broken bpndin one rail will tend to unbalance the distribution of the propulsion current in the rails, -and-also to introduce an abnormal resistance in the rail circuit... To detect the presence of 'such' faulty'insulatonand rail bond, test equipment .is mounted; upon. a locomotive 1.0 of the railway,. and which locomotive is normally provided. with. a, trolley pole T? for collecting propulsion current from the trolley wire for operatingthe motors of thelocomotive, the motors being omitted from thesdrawingsince they are not requir'edfora .fnlll understarding of the present invention-s The locomotive L0 is provided with a source periodic or alternating current. such source being indicated. conventionally at OS. This source OS may be. anyone/of several forms and may mean electron tube oscillaton. By way of illustration; I shall assume. that the source OS supplies a currentof the frequency of the order of, say, 110,000 cycles per second,v but other frecurrencies:- can be used. The output: of the oscillatorOS; is supplied to. a primary winding H of a transformer Tl, a secondary winding l2 of which has one terminal connected to the trolley pole 'I'P througha capacitor 1 3 and a conductor [4. and its-other terminal connected to the rails la and lb; through a conductor liconnected to the frame and wheels of thelocomotive. Thus the alternating current supplied 'by'the oscillator OS is. applied between the trolley wire. TW andthe rails and will cause current'to- -flow in the trolley wires out from the locomotive andreturn through the track rails: in multipl'e due to the distributed capacitance of the trolley wire and rails.

To aid the flow of the carrier or high frequency alternating current, a temporary connectionincluding a capacitor l6 may be connected between the trolley wire and the track rails, but ordinarily such temporary connection would not be required.

receiving unit RU is provided for the locomotive LO. The unit RU is adaptable of being carried on an. auxiliary trolley pole ATP mounted on the locomotive withitwo swivel joints H and i8 so that the unit" RU mounted on the upper joint l8. will always ride onthe trolley wire in the same position. The unit RU is formed with a housing or case 9- of suitable insulating material toprotect the enclosed elements, tobe shortly referred to, from weather and from the propulsion current. Preferably; at least two wheels 20 and 2! are journaled' in the housing 9 to follow the trolley wire and assure that the unit RU always has a definite position with respect to the trolley wire. Two pick-up coils 22' and 23 are. mounted in'the case 9. These two pick-up coils 22 and 23 are preferably alike and are symmetrically spaced so that the two coils will have as des substantially the-same inductive relationship to the trolley. wire, thei'qtwo coils being; spaced a given distance apart'along the trolleylwires Capacitors 24 and 25 .aret connected across thepickup coils 22and 23, respectively, to'tunethe. coils to the frequency of the alternating current supplied by the oscillator OS and to suppress voltages induced in the coils due to noise and other energy flowing in the trolley wire. 7 l

' .Thettwo pick-upcoils 22 and-23 are connected one to each of two receiving circuits, the circuit for the coil 22 including the topterminalof the coil, wire 26,; left-hand portionof a resistor Rl'as viewed. in Fig. 1, to an intermediate; adjustable terminal 21, a tuning coil,28, wires 29,and 30, and-the lower terminal of the pick-up coil 22, and the circuit for the pick-up coil 23 including top terminal of the'coil, wire 3|, right-hand portion' of resistor RI to intermediate -terminal ;21, tuning coil 28,..wires29 and 32, and the lower terminal of the coil. The pick-up coils 22 and 23 are disposedand wound so that when an alternating current flows in the trolley wire TW the electromotive forces induced in the coils cause at a: given instancethe top terminal ,of coil 22 and theglower terminal of coil 23, as. viewed in the drawing, to be positive,- and at the next instant the lower terminal of coil 22 and thetop terminal of coil 23 to be positive. It follows that. the currents tending to flow ,in the tuning coil 28 due to the electromotive forces induced inthecoils 22 and 23 oppose eachother and will balance out when the same value of alternating current flows in the trolley wire past each of the pick-up coils.

The tuning coil 28 isprovided with an adjustable The test equipment of the locomotive LO includes an indicator which is disclosed as a twin electron ray tube ET of the indirectly heated type. The tube ET- is provided With-a cathode 34, two control electrodes or grids and: 36, an anod 3], and a targetelectrode 38.. ThetubezETl is powered from a source on the locomotive, not shown, but having positive and negative terminals indicated at B190 and :Nlllfl, respectively. fIhe anode 3i and the target-electrode;'38 are connected to the positive terminalBlllU of the power source in the usual manner, resistors R4 and R5 being interposed in the'connectiondn the customary arrangement. Cathode 34 is connected to the negative terminalrNIOD of thesoi1rce-rto complete the usualanode circuit-. Control grid 35. and cathode 34 are connectedracross the'tuning coil 28. and capacitor 33. Consequently, when a zero voltage exists across'the tuningcoil- 28no control voltage is applied to the'xcontrol': electrode 35 of the tube; and substantially'no shadow angle of the corresponding section of the tubeET is created. Thuswhen the locomotive L0 is movlng along a stretch of the railway track, and the insulators lllof the difierent hangers areall in good condition, 'equal electromotive forces are induced-in the pick-up coils 22 and23, these two electromotive forces cancel each'other in the two receiving circuits so that zero voltage exists across the tuning co'il =28,fand' substantially no shadow angle is indicated for 'the corresponding section of the indicator tube ET. Assuiningthat,- as the locomotive LO moves along theltrack, a hanger, such as thecenter hanger showndn Fig. 1', comes between the two pick-upcoils 22 and-.23, and in which hanger the insulatorllll is short circuited, a relatively large portion ofthe alter-, nating current supplied by the-source OS will leak to ground through the faulty insulator with the resultthat. the current flowing in the trolley wire past pick-up coil .22 is larger than the current flowing in the trolley wire atpick-up coil23. This causes the electromotive force induced in coil 22 to be larger than that induced in coil 23, and a voltage equalto the difference of these two elec tromotive forces appears across the tuning coil 28 and is applied'to the control electrode 35 0f tube ET causing the display of a corresponding shadow angle for the corresponding section of the electron ray tube ET. Thus the operator of-qthe locomotive LO having the tube ET mounted vis; ually before him is informed whenever the loco motive passes under a .hanger-havingla broken down-insulator. v a I To detect broken rail joint bonds, thelocomoe tive L0 is provided with twopick-up coils 4|] and 4| mounted on the locomotive for inductive rela: tionwith the rails Iaandlb, respectively,-as clearly indicated in the right-hand portionof Fig. 1. Coils 40 and 4| are preferably alike and are disposed to have like inductiverelationship with the respective rails. That is, the alternating current flowing in the rails in multiple with an equal value of current in each rail will induce electromotive forces of equal value in the two pick-upcoils 40 and 4|. Each coil 40 and4| is connected to a receiving circuit, the circuitfor coil 40 being traced from the left-hand terminal of the coil through wire 42, the lower portion of aresistor R2, as viewed in Fig. 1, to an inter mediate adjustable terminal 43, a tuning coil 44 and wire to a junction terminal ofthe two coils 40 and. Similarly, the circuit for the piclr up coil 4| can be traced from the right-hand terminal of the coil through wire 46, top portion of resistor R2 to intermediate terminal 43, coil 44 and .wire 45 to the junction terminal of the' two pick-up coils. The tuning coil 44 is provided with an adjustable core or otherwise made adjustable to tune the two receiving circuits to resonance of the frequency of the alternating current supplied from the oscillator OS. A capacitor 4? is connected across coil 44 to aid in tuning the associated receiving circuits and to bypass noise energyof frequency other than that Iofthe test current. By proper positioning of the intermediate terminal 43 along resistor R2,'the two receiv-- ing circuits are in balance. The connections for the pick-up coils 40 and 4| are such that the electromotive forces induced therein by the testing current flowing in therails in multiple tend to cause currents to flow in oppositedirections through the tuning coil 44, and the two currents cancel as long as the testing current is of equal value in thetwo rails. The tuning coil 44 is connected across control electrode 36 and cathode 34 of the tube ET by an obvious circuit. .Thus when the locomotive L0 is moving over a track in which the rail bonds are in goodcondition and an approximately equal value of the testing current supplied by the oscillator OS flows in each rail, equal electromotive forces-are picked up by-the coils 40 and 4| and the voltages applied to coil 44 by the two corresponding receiving circuits will balance out and no-control voltag'cis applied to the-control electrode 35 oi tube- Ei? amped with theresult no shadow ngie appears for corresponding section or thetube.

It a rail joint having a broken rail bond- 1s apmached. the current of the oscillator OS will be greater in the rail not having the broken'bond, and thus the electro'motive forces induced in the coils 40 and 4| will be unequal. 'A voltage equal to the diilference of the two electromotive forces is now developed across the coil 44 and a corresponding voltage is applied to control electrode Ii so that a corresponding shadow angle is displayed in the corresponding section of the tube ET. This means that there is displayed a specific indication at the electron ray tube ET to the operator of the locomotive whenever the loco motive passes over a rail joint having a broken rail bond.

To sum up the operation of the test equipment of Fig. l, the (me'rator of the locomotive LO sets the oscillator OSinto operation to supply testing current to the trolley Wire and rails and then runs the locomotive slowly over the mine tracks. Between adjacent hangers and on stretches where the insulators of the hangers are in goodco'ndition, no indication is displayed at the indicator tube When the locomotive LO passes a hanger having a short circuited or defective-in sulator that permits current to leak from the trolley wire into the mine roof, an indication of such condition is displayed in one 'sectionof the tube ET. When the locomotive passes a rail joint having a broken rail bond, then an indication of that condition is displayed in the other section of the tube Thus the operator by'obser'ving the two shadow angles of the tube ET as the locomotive is operated overthe tracks can detect the broken down trolley wire insulators and broken rail bonds.

in Fig. 2' a modificationof the portion of the equipment for testing rail bonds is disclosed. 'A mine locomotive L is indicated conventionally as traveling over the rails Ia and lb of the mine track MT, and this locomotive is provided with the pick-up coils 40 and 4| for receiving electr'o motive forces dueto the alternating test current applied to the trolley wire and rails the same min Fig. l. The pick-up coils 40 and M of Fig.2 are connected to tuned receiving circuits, the circult for coil 40 including'capacitor 50 and input terminals of a full wave rectifier the output terminals of which rectifier are connected across the lower portion of a resistor R3 and an indiactor A. Similarly, the receiving circuit for pickup coil 4! includes a capacitor 53 and input "terminals of a full wave rectifier 54, the output terminals of rectifier 54 being connected across the upper portion of resistor R3 and. indicator A. The connections for the output terminals of the rectifiers 5| :and 54 are such that current from rectifier 5| tends to flow through the indicator A from right to left and the lower portion of resistor R3, and the current from the rectifier 54 tends to flow through the upper portion oflre-y sistor R3 and indicator A from left to right. When equal portions of the alternatingtest current flow inrails la and lb, the two rectified'currents "applied to indicator A are-equal and rapposite and cancel, causing the indicator to display a hero reading, The terminal 52 of the resistor R3 is made adjustable to normally "condition the two circuits for the indicator A to give a zero reading. If the locomotive LO of Fig. 2 is moving along the track and a broken rail bond or 21131101?- mally high resistance bond is encountered, the toil; current will be unequal in the tworails, and

the

the unequal eiectromotive'tors induced in the pick up coile fld and Al will cause a correspond ing currentito -llow in one direction or the other tlirough ithe' 'indicator A with the result that indicator A"'Wiil display a corresponding indication; lt is obviousirom the foregoing that the apparatus'offi'g. 2 can'be usedin the equipment of :Fig. :1 in that portion or the test equipment for testing broken rail bonds. Itls to be pointedout that for testing rail bonds only the apparatus of Fig. 2 can be arranged for the source-or alternating current, such as oscillotor'OS' of' Fig. l, to be'connected to a coil mounted above one rail or two coils, one mounted above each rail at the end of the locomotive oppositethe position of the'pick-up coils 40 and II and the test current applied to the rails by electromagnetid induction. The test current then flows in the-rails inmultiple and returns through the'g round due to the distributed rail to ground impedance; v

It is also to be observed that with test equipnient here disclosed, the locomotive can be provided with a paint or whitewash type of marker under the control of the operator, and the operator can leave a telltale mark on the ties or other ortions of the track at locations of faultytrolley wire insulators and rail bonds as an aid to the repair crew.

It is apparent that that portion of the equipment for testing the trolley wire insulators can 'be'used alone or 'that portion for testing the rail bonds can be used alone.

Test equipment-here disclosed has the advantages tha'iz the trolley wire insulators and rail bonds can be tested accurately and with dispatch.

Although -I have herein shown and described only-certain forms of equipment for testing trolley wire insulators and rail bonds of electric railways-embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention;

Having thus described my invention, what I claim is: l

1. In test equipment for an electric railway, the combinationcomprising, a source of alternating current of relatively high frequency mounted on a vehicle of said railwayan'd having connections to the propu lsion conductor and to the track rails to cause alternating current to flow in said pro msion conductor from said vehicle and return through the-track-rails in multiple, a pair of receiving circuits-on said vehicle each including a pick-up coiLsaidpick-up coils mounted one over each .trackirail; said pick-up coils alikeand disposed for substantially like inductive relationship to the respective rails, a tuning coil on said ivehicle, said recelving'circuit differentially connected across said tuning coil to create a voltage across the tuning coil when unequal values of said alternatingcurrent flows in the track rails, and. an indicator connected across said tuning coil responsive to such voltage.

' :2. In; test equipment. tor an electric railway having a propulsion circuit which includes a trolley wire and bonded track rails, the combination comprising, a; source of alternating current mountedon a vehicleof said railway coupled to the trolley wires-and the track rails of the pro- :pulsion circuit .of; said railway to cause substantially equal values of alternating current to flow in the track rails under normal condition of the railibonds, a pairmrpick-up coils on said vehicle they are difierentially connected to create a voltage across the impedance element when unequal values of said alternating current flows in said rails due to an abnormal condition of a rail bond in one of the rails, and an indicator carried on said vehicle and connected to said impedance element to detect the voltage thus created across the impedance element.

ANDREW J. SORENSEN.

10 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 574,333 Heilholtz Dec. 29, 1896 1,796,427 Austin Mar. 17, 1931 1,908,297 Anderson May 29, 1933 2,154,156 Turner et al Apr. 11, 1939 2,471,417 Dimmick et a1 May 31, 1949 2,475,680 Sorensen July 12, 1949 

